1. Field of the Invention
The present invention relates to a developing device including a developer regulating wall for regulating an amount of developer falling along a transport direction of a developer transport path, and an image forming apparatus including the same.
2. Description of the Related Art
In recent years, the sizes of an electrophotographic copying machine, an information recording apparatus, and the like are getting smaller and smaller. With the trend toward a downsized developing device and a smaller developer containing capacity so that multiple developing devices can be provided within a limited space around an electrostatic latent image bearing member, it is becoming common practice to separately provide a developer supply portion (hereinafter, referred to as “hopper”). In this case, the supply of the developer from the hopper to the developing device is ideally performed evenly throughout an axial direction of a developer carrying member, but in actuality, in terms of space, the supply of the developer to the developing device is performed by supplying the developer within the hopper through a developer supply port provided to one end portion of a developer transport path.
In an apparatus of the related art, for example, as illustrated in FIG. 11, the developing device includes a developer regulating wall 3 having an upper rim portion 2 for regulating an amount of fall of the developer when the developer transported by a transporting screw falls from the developer transport path 1 along the developer transport direction of the developer transport path 1. The upper rim portion 2 of the developer regulating wall 3 is inclined so as to become lower in height toward the developer transport direction of the developer transport path 1 so that the developer is supplied substantially evenly in the axial direction of the developer carrying member.
Replenishment with the developer is intermittently performed to thereby prevent uneven replenishment with the developer inside the developer container in terms of the longitudinal direction due to an image ratio of an original.
As described above, the developer regulating wall 3 has the upper rim portion 2 for regulating an amount of the developer falling from the developer transport path 1 along the developer transport direction of the developer transport path 1, and the upper rim portion 2 is inclined so as to become lower in height toward the developer transport direction of the developer transport path 1. That is, because the developer regulating wall 2 has such a shape as to become lower in height from a front side toward a rear side when viewed from an operator, the developer supplied from the hopper falls little by little starting from the front side, while the developer remaining without falling is transported toward the rear side by the transporting screw and falls at a transport destination. By repetition of this process, the developer replenished from the hopper is supplied with a specific distribution along the longitudinal direction (hereinafter, the distribution is referred to as “distribution of the amount of fall”),
At this time, the developer having a low agglomeratability has a small angle of repose. In contrast, the developer having a high agglomeratability has a large angle of repose. In view of the difference, a technique for determining a width of the upper rim portion 2 of the developer regulating wall 3 and replenishing the developer Substantially even in the longitudinal direction with a Certain width within the developer container irrespective of the agglomeratability of the developer is disclosed (see Japanese Patent Application Laid-Open No H08-137235).
However, when the developer having an excessively agglomeratability is supplied, the developer transported within the developer transport path 1 cannot climb over the developer regulating wall 3 in its high position, and a large amount of developer falls on a downstream side of the developer transport path 1 in the longitudinal direction. As a result, the amount of fall of the developer is larger on the rear side of the developer container. In contrast, when the developer having an excessively high agglomeratability is supplied, the developer transported within the developer transport path 1 climbs over the developer regulating wall 3 in its high position, and a large amount of developer falls on an upstream side of the developer transport path 1 in the longitudinal direction. In any one of the cases, the supply of the developer within the developer container toward the longitudinal direction becomes one-sided, which causes image degradation ascribable to unevenness of the distribution of the amount of fall of the developer.
A change in the agglomeratability (flowability) of the developer is ascribable to a use environment, an unattended environment, a deterioration condition of the developer, and other such causes, but in the following description, the phenomenon is described only with the agglomeratability (flowability) without specifying the use environment or the like. As illustrated in FIG. 8, a larger amount of developer with the agglomeratability of the developer being higher than a central value falls on the front side of the developer container, while a larger amount of developer with the agglomeratability of the developer being lower tends to fall on the rear side. This causes image degradation corresponding to the distribution of the amount of fall within an image. Specifically, a change in an image density is smaller in the position in with a larger amount of developer falls, and a difference in density per sheet on an image become larger in the position in which the amount of fall of the developer is smaller as the number of printing sheets becomes larger. Further, a phenomenon in which an extraneous substance adheres to the developer in advance occurs on a surface of the developer carrying member which is opposed to the position in which a larger amount of developer falls, which tends to cause image degradation.